Mammaglobin is a breast-specific gene that has shown promise as a new marker for the specific detection of breast cancer. There are several important features that make mammaglobin an ideal candidate as a marker for breast cancer detection. One, it is a breast-specific gene, therefore mammaglobin's detection outside the breast indicates breast cancer disease. Secondly, the high percentage of primary breast cancers that are mammaglobin positive (more than 80%), and an equally high percentage expression pattern in metastatic breast cancer, make mammaglobin a promising candidate marker gene for breast cancer detection. Thirdly, mammaglobin is a secreted protein of low molecular weight, and preliminary data indicate its presence in the sera of some breast cancer patients. Therefore, mammaglobin may have utility as a serum marker for breast cancer detection. The immediate goals of this study will be to: 1) Using the ELISA assay for the serum detection of mammaglobin, we will evaluate and establish mammaglobin levels in normal women. This aim will help establish baseline values in both pre- and postmenopausal women, pregnant women, and explore factors that may modify mammaglobin levels. 2) Using the ELISA assay, we will evaluate the levels of mammaglobin in breast cancer patients and correlate this data to the primary tumor using immunohistochemical examination for mammaglobin. The presence of circulating breast tumor cells will be examined using a specific RT/PCR analysis of buffy coats from these samples. 3) Test the hypothesis that mammaglobin expression in blood by ELISA and/or RT-PCR will predict response to therapy and predict relapse in patients with mammaglobin expressing breast tumors. The scope of this proposal is to address whether mammaglobin protein can be detected in the serum of women with breast cancer and determine if serum detection of mammaglobin has any correlation to breast cancer when compared to normal control groups.